Linux-Hams archive - May 1998: RE: Watchdog
RE: Watchdog
Charles Greene (tiphlph.szkhwf@swan.ac.uk)
Fri, 08 May 1998 08:47:33 -0400
At 05:53 PM 5/6/98 -0400, Patrick Ouellette wrote:
>
>> -----Original Message-----
>> From: omq.ozoxhsfn@cite.net
>> [mailto:terhi.victor@logonet.com]On Behalf Of Charles Greene
>> Sent: Wednesday, May 06, 1998 4:11 PM
>> To: Patrick Ouellette; Joe Martine; sboef@mtu.edu
>> Subject: RE: Watchdog
>>
>>
>> At 12:16 PM 5/6/98 -0400, Patrick Ouellette wrote:
>> >I've thought of a similar setup. Diodes to handle the current can
>> >be hard to find/expensive,
>> Not true. Radio Shack, # 276-1181, $2.69. 25 Amp, 50piv full
>> wave bridge rectifier (use one leg). Any electronics parts store
>> has a single diode, for less. Don't forget a heat sink and
>> mounting hardware, if needed.
>
>I was thinking the UPS might need more than 25 Amps depending on the
>load connected.
>
Well, its easy to find higher current diodes for reasonable prices.
>>
>> > so I thought of using a spdt relay with
>> >the coil connected to the AC that would connect the battery when
>> >the ac drops out. The advantage I see here is the circuit that
>> >connects the batteries uses no power and has no voltage drop
>> >while you are on batteries.
>>
>> There are problems connecting batteries in parallel. See my
>> previous posting.
>
>The batteries would not be in parallel - the internal battery
>could be connected to a relay that would drop when the external
>battery kicked in. Maybe triggering the relay with the low battery
>signal and making sure it latches until the AC is restored. Of
>course latching relays are more expensive and harder to find.
Use a DPDT relay and latch the relay through one set of contacts, if you are powering it through DC. If it is an AC relay across the line or a DC relay powered by the AC line power that closes when the AC goes away, you don't need to latch it.
>You
>would want a small amount of time where both batteries we connected in
>parallel to keep the UPS output from dropping during the transfer.
>
Use the diode auctioneering circuit to do this. You will probably find you don't need the relay, if you use a large enough diode.
>If the UPS cleared the low batt indicator, and the PC was monitoring it,
>the system should be able to run until the external battery is spent -
>retriggering the low batt signal and causing a hopefully orderly
>system shutdown.
>
>> >
>> >I have been working on a similar system to keep my rig powered when
>> >I loose AC while the AC is on (actually while my 12v power supply is on since the
>> >relays I am using have 12v DC coils), and to the rig when the AC drops.
>> >The radio doesn't seem to mind the momentary power glitch when the
>> >relay drops.
>>
>> The computer might not like it, if directly connected, but the
>> UPS should take out the glitch, if I understand correctly that
>> you are using the UPS and just using the other battery to extend its life.
>
>Actually I am not using a UPS right now - I have the setup on
>my 12V DC radios only.
I used a similar arrangement on our repeater, to switch from the AC power to the batteries (two heavy duty six volt batteries in series). I tried both the diode actioneering circuit and the relay and both worked. I had hoped that the relay would drop off on battery undervoltage, about 10.5 volts, to protect the batteries, but the relay wanted to stay closed until the batteries were down to just a few volts; I don't remember how low, but it wouldn't have accomplished the purpose of protecting them, although it switched the batteries in ok. There was a battery control device in QST 3 or 4 years ago which would have worked well in this instance. So, either way will work, and with an external control circuit, you can make it do about anything you want it to.
-------------------
Be nice. It doesn't take any longer.
-------------------
Charles Greene
Internet=zqedrn@relay.tunkki.fi
Internet to Amprnet=terhi.victor@logonet.com
115 Aaron Avenue
Bristol, RI (On the shore of beautiful Narragansett Bay)